1. Field of the Invention
The present invention relates to a cutting/expanding tool that permits the in-place replacement of an existing main by inserting the cutting/expanding tool into the main so as to cut the main and expand it, thereby permitting a replacement main to be drawn through the existing main.
2. Description of the Related Art
When it becomes necessary to replace an existing main, for example a gas service main and particularly a buried gas main, it is often desirable to leave the existing main in place and to use is as a guide for the replacement main. In the particular case of a buried main, the location of the main, for example under a sidewalk or a street, often makes excavation costs prohibitive. Moreover, even if excavation is undertaken, the cost to restore the surface of the ground, for example by repaving, often contributes substantially to the overall cost of repairing the main.
Various techniques have therefore been proposed to permit the replacement on an existing main without the need for excavating the entire length of the main or otherwise disturbing the surface of the ground. According to these techniques, the ground at two ends of the existing main is excavated to expose those ends. A tool is inserted into the buried main to cut and to expand the main in place. A replacement main is drawn through the expanded main, leaving the old main in place in the ground.
U.S. Pat. No. 3,181,302 to Lindsay shows such a tool. As shown in FIGS. 9 through 11 therein, the tool includes a pipe cutter that pulls a spreader assembly. The pipe cutter is formed by two half cylinders which are retained in spaced relationship and which support a plurality of cutter disks. The disks alternately project upwardly and downwardly from the surface of the cylinder halves. With this structure, as the pipe cutter is drawn through an existing main, it progressively cuts the main in half whereupon the spreader assembly spreads the halves to permit a replacement main to be drawn back through the existing main's halves.
A disadvantage of the cutter/expander tool shown by Lindsay is that it is prone to rotational motion which causes unpredictability in the cut. The rotational motion is so large that Lindsay provides a rotating bearing to accommodate the motion. Moreover, the Lindsay tool cuts the existing main into two halves, and separates the two halves with its spreader. With no support at the separation between the halves, the soil surrounding the existing main easily falls into the cavity left by the cutter/expander tool. This soil blocks efforts to insert a replacement main into the existing main.
It has also been considered to use a cutter/expander tool in the form illustrated in FIG. 26. As shown there, the tool includes an expander bulb 1 in the form of an eccentric, generally conical bulb. On the expanding side 2, a shearing blade 4 is mounted through suitable means such as bolts 5. The shearing blade 4 is located at a diameter on the eccentric expander bulb which corresponds to the diameter of existing main 11. Means 6 are provided on the expander to push or pull (not shown) the tool through the main 11.
Use of the cutter/expander of FIG. 26 has not been found to be satisfactory. First, like the cutter/expander of Lindsay, it is not possible to control rotation of the tool. Thus, even though the FIG. 26 tool is inserted into the main with shearing blade 4 down, it may eventually rotate to a shearing blade-up position, thereby allowing surrounding soil to fall into the existing main and block the insertion of a replacement main. Second, the force required to overcome friction and to create a cutting force while propelling the tool through the existing main is so great as to force the existing main out of the ground. Usually, the existing main is forced out of the ground into the excavation ditch at the exit end of the tool. Sometimes, however, when the tool binds within the existing main, the existing main buckles up through the ground at its midpoint, thereby defeating the entire purpose of using the tool.
Finally, the tool of FIG. 26 is ill-equipped to cut through many different couplings and repair points often found on existing mains. As shown, for example, in FIG. 1, main 11 can include a significant number of couplings and joints along its length. For example, a stainless steel repair sleeve 12 may have been bolted around the main to repair a leak in the main. The main may also include a strap-on T coupling 14 which permits services 15 to be added at any point along the main. Additionally, to connect separate lengths of main together, threaded couplings 17 or compression couplings 19, may have been used. Such couplings present problems to conventional cutting/expanding tools.